The use of modular jacks and plugs for data transmission is common. Jacks receive the plugs that are attached to the ends of an electrical cable. Jacks are mounted to, and are an integral part of electronic devices such as switches or routers in the data centers or computers in offices. The cable is terminated by plugs, and the electronic equipment has to have jacks corresponding to the plugs. Plugs and jacks are designed to be able to mate to provide both mechanical and electrical coupling. In premise wiring systems, the jack may also be connected to cables as a free hanging connector.
The electrical cables have multiple conductors or wires. For Ethernet connections, typically eight wires are used. The electromagnetic signals within each mated pair travel from the equipment side to the cable side and vice versa, using designated contact pairs such as 1-2, 3-6, 4-5, 7-8. Mechanical dimensions of the plug and the jack and their interface are governed by international standards. In the case of the connectors employed in the Ethernet signal transmission, the governing standards are International Electrotechnical Commission (“IEC”) standards 60603-7 series.
From the transmission point of view, the jacks, cable and plug represent components of a channel. The channels and corresponding components performance are referred as classes and categories specified in the IEC/ISO 11801 standards shown in the following table:
ISO/TECANSI/TIA-568-C.1FREQ. MAX.11801CATEGORYCHARACTERIZATIONClass C3 16 MHzClass D5e 100 MHzClass E6 250 MHzClass EA6A 500 MHzClass F7 600 MHzClass FA7A1000 MHzClass I8.12000 MHzClass II8.22000 MHz
A common mechanical connector configuration known as RJ45 (described in the IEC60603-7 series of standards) allows for connections between 40 GbE (Gigabits per second of Ethernet frame transmission) and lower speed equipment through a feature called auto-negotiation. During the auto-negotiation process, both devices assume the master-slave relations and agree on the maximum speed for data to be transmitted.
The channels should be able to support the Ethernet protocols and may affect the auto-negotiation. Electrical cables may be connected to plugs and plugged into jacks disposed within the various generations of Ethernet equipment. However, channels designed to older Ethernet speeds will slow down and force the newer and faster networking equipment to run below its intended speed. There are no known modular connectors that work in the wide spectra from 10 to 2000 MHz without causing some degradation of the signals.
As previously noted, the Ethernet protocols divide the signal into four streams which are transmitted over the same cable. Thus, with a mated connector pair there are also four streams of signals operating simultaneously. The unwanted interaction of these signals called Near End Cross Talk (or “NEXT”) has to be minimized to allow error-free transmission. The most common means of reducing the NEXT is compensation. Compensation is a method of creating NEXT of similar amplitude but opposite polarity from the NEXT created at the interface between the jack and the plug.
Signal degradation at high frequency is caused by several mutually dependent issues. One issue is where the primary compensation is too far away from the interface, causing an unpredictable phase shift of electromagnetic signals traveling within the jack-plug mated connectors. Another issue is that the plug contact blades have high intrinsic self-inductance, and uncontrolled and relatively low capacitance between adjacent contacts. The jack should compensate for the plug inductance and capacitance. Conventional designs include a board that adds compensation at the tips of the contacts, but the electrical length between the contact point and the compensation is too great to completely cancel the plug inductance and capacitance in both phase and magnitude.